Aim of the study
This study was conducted to determine factors affecting antihypertensive medication adherence in Upper Egypt.
Design of the study
From September 2015 to September 2019, we conducted a large cross-sectional multi-center study among 2420 hypertensive patients attending the out-patient cardiac clinics at three different university hospitals (Sohag, South Valley, and Beni Suef University Hospitals). All subjects provided a written informed consent to participate in the study. The study protocol was approved by the ethical committee at the universities where the study was conducted.
Data was collected through a personal interview with the patients using a modified non-adherence to treatment questionnaire [11] to cover a variety of items including socio-demographic factors (age, sex, marital status, occupation, education level, income, residence, number of pills, and associated comorbidities such as diabetes, dyslipidemia, and cardiovascular diseases) as predictors of adherence with medication regimen and behavioral factors (missing doses of medication, lack of motivation to be cured, not having enough time for exercise, lack of complying with dietary regimen, and lack of motivation to stop smoking) as causes of non-adherence with medication regimen. Adherence was calculated only for antihypertensive medications, and concomitant medications, such as for diabetes or dyslipidemia, were not considered.
Income was classified into three categories according to the individual income per year 1, low income (less than 8827 Egyptian pounds); 2, moderate income (from 8827 to 58900 Egyptian pounds); 3, high income (more than 58900 Egyptian pounds) [12, 13]. Level of education was classified into three categories 1, illiterate; 2, primary/secondary; 3, higher (university).
A pilot study was carried out on 300 persons chosen randomly (100 patients at each University Hospital) to estimate the time required for each interview and to identify difficulties that may arise, how to deal with and how to organize perfectly the field of work.
Medication regimen adherence was composed of 8 items, asking how often the patients forget to take their medicine: (1) How often do you forget to take your medicine? (2) How often do you stop taking your medicine because you feel better? (3) How often do you stop taking your medicine because you feel worse? (4) How often do you stop taking the medication because you believe that they are ineffective? (5) How often do you stop taking your medicine because you fear side effects? Or have caused side effect, dizziness/weakness. (6) How often do you stop taking medicine because you try to avoid addiction? (7) How often do you stop the medication because you are using traditional medicine (healer) or religious belief? (8) How often do you stop the medication because of cost of medication? The responses were measured on a 4-point Likert scale: (1) every day, (2) frequently, (3) rarely, and (4) never. Lifestyle modification adherence had 4 items: (1) How often do you smoke? (2) How often do you engage in physical exercise? (3) How often do you eat table salt? (4) How often do you eat meat with high animal fat? We excluded a question asking about alcohol consumption, as all the participants denied consuming alcohol at all, and this could result in a bias of the adherence rate, as all the participants will get 4 points for this question. In our community, even if the patient is consuming alcohol, he may deny that due to social, traditional, and religious factors. So, our questionnaire was composed of 12 items [10, 11]. Participants were asked to respond to the single question based on a 4-point Likert scale: how often desirable or undesirable behaviors relating to the control of hypertension. The responses were (1) every day, (2) frequently, (3) rarely, and (4) never. Some questions were set such that the response “every day” did not reflect the worst scenario of non-adherence, but it reflects the best scenario. To resolve this, these scores were reversed, for example, how often do you engage in physical exercise (4) every day, (3) frequently, (2) rarely, and (1) never
The 12 items measuring treatment adherence and lifestyle modification adherence were added up to get a sum index with a distribution ranging from 21 to 48 with mean 34 (SD = 5.31), and median split was 34, so the cutoff point of the adherence score for the participants was 34 (70%), which was dichotomized into two gatherings, i.e., 1—those who are non-adherent (≤ 34) and 2—treatment adherent (> 34).
The following formula was used to calculate the minimum size of the required sample for each of the three sites (universities) where the study was conducted:
$$ n={\left(\mathrm{z}\right)}^2\ p\left(1-\mathrm{p}\right)/{\mathrm{d}}^2 $$
where n indicates the sample size, z indicates the level of confidence according to the standard normal distribution (for a level of confidence of 95%, z = 1.96), p indicates the estimated proportion of the population that presents the characteristic (about 26%), d indicates the tolerated margin of error (for example, we want to know the real proportion within 5%).
Using the previous formula for the sample size calculation (n) = (1.96)2 × 0.26 (1−0.26)/(0.05)2 = 296. So, the minimum sample size is 296 participants.
Participant characteristics
All hypertensive patients aged ≥ 18 year, taking antihypertensive treatment for at least 1 month ago and who agreed and consented to participate in the study were included.
Analysis of data
The following formula was used to calculate the minimum sample size: n = (z)2 p (1−p)/d2 as prescribed in the “Methods” section.
The data was analyzed by the SPSS version 19 program for data entry and analysis; information was summarized using frequency tables and cross tabulations. The chi-squared test was used for categorical variables and t test for continuous variables. Univariate and multivariate binary logistic regression was done to detect socio-demographic and behavioral factors significantly associated with non-adherence. Odds ratio (OR) at 95% confidence interval (CI) and p values were computed. P value was considered significant at or below 0.05.
The outcome variable was treatment adherence, which is comprised of medication regimen and lifestyle modification adherence.